Caffeine is a stimulant that acts directly on the central nervous system, and according to the Food and Drug Administration, it can be considered both a drug and a food additive. It is widely used in food and beverages designed to increase levels of alertness, such as coffee and soda. Caffeine is also useful in biomedical research, as it increases intracellular levels of cAMP, a signalling molecule in many biological processes. Knowing how to prepare a simple 1 millimolar solution is an essential skill for chemistry and biology students at any level, and with the right supplies and a little knowledge, preparing a 1 millimolar caffeine solution becomes an easy task.
Calculations
Step 1
Determine the volume of 1 mM solution you wish to prepare. As an example, you can will prepare 100 milliliters, or mL, using water as the solvent.
Step 2
Determine the amount of caffeine needed to prepare 100 mL of 1 mM caffeine solution. This can be easily calculated by using Resource 1 and entering this information in the "Mass from volume & concentration calculator." The formula weight of caffeine is 194.19.
Step 3
Calculate the mass necessary, which is determined to be 1.9419 milligrams, or 0.0019412 grams. As the analytical balance is limited to four decimal places, this amount must be rounded to 1.9 milligrams or 0.0019 grams.
Measuring Out Reagent and Solvent
Step 1
Use a graduated cylinder to carefully measure out 100 milliliters of water.
Step 2
Place a piece of weighing paper on the analytical balance and "Zero" the instrument. Use your scoopula and the container of solid caffeine powder to measure out as close to 0.0019 grams as possible.
Step 3
Place a clean 250 ml beaker next to the analytical balance.
Combine and Store
Step 1
Transfer the caffeine powder from the balance to the beaker.
Step 2
Pour the water gently from the graduated cylinder into the beaker containing the caffeine powder.
Step 3
Stir the solution in a circular motion, using your stirring rod, until the solid caffeine powder is dissolved.
Step 4
Transfer your completed solution to a storage container and seal it with a lid.
Step 5
Label your solution appropriately: "Caffeine - 1 mM aqueous solution"
Tips and Warnings
- Depending on the equipment you have available, it is often easier to make a stock solution of a higher concentration, and dilute down to the desired concentration.
- Caffeine use can result in overdose and death. Caffeine should only be consumed in food and beverage products certified by the FDA as fit for human consumption.
Things You'll Need
- Analytical balance
- Weighing paper
- Pure caffeine powder (CAS 58-08-2)
- Graduated cylinder
- Scoopula
- Glass stir rod
- Beaker
- Calculator
- Storage container
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